How to Stop Crocosmia Spreading and Take Back Control of Your Garden

As a passionate gardener, I adore crocosmia. Their vibrant spikes of color livening up my garden beds in summer are always a welcome sight. However, as much as I love these fiery flowers, they do have a habit of spreading rapidly and taking over.

If left unchecked, crocosmia can quickly turn from a delightful addition to a rampant invader Their stolons creep stealthily under the soil, and seemingly overnight, a single clump becomes a thick carpet smothering everything in its path

Fortunately, with some knowledge and a little elbow grease, it’s possible to stop crocosmia in its tracks and reclaim your garden. Here are my top tips for controlling these creepy-crawly corms and preventing them from spreading out of control.

Monitor and Remove Unwanted Growth

Keep a close eye on your crocosmia patches, especially in spring and early summer when growth explodes. Remove any shoots sprouting up where you don’t want them It’s much easier to pull or dig out small clumps rather than waiting until they get established and form a tangled mat of corms and stolons

Check around the edges of existing clumps and thoroughly weed the surrounding area. Stolons can travel many feet underground before popping up, so be vigilant. Patrol farther afield too – I’ve found crocosmia shoots up to 20 feet away from the mother plant!

Cut Back Foliage in Fall

Chopping off the dying foliage in fall prevents the plant from photosynthesizing and storing energy in its corms for next year’s growth spurt. While this won’t kill the corms, it will weaken them and slow down their spread.

I use secateurs to snip the leaves and stems back to ground level once they start yellowing after bloom. Remove all greenery – don’t leave anything sticking up for the crocosmia to keep feeding on.

Dig and Divide Overgrown Clumps

Every three to five years, dig up the dormant corms in early spring, break them up into individual corms and replant in smaller groups. This helps reduce their vigor and restricts how far they can spread via stolons.

Use a garden fork to lift the clump out carefully, trying not to break up the chain of corms. Gently tease apart the corms or cut the stolons with a sharp knife. Replant only a few corms together, spacing the groups at least 18 inches apart. Discard excess corms or give them to gardening friends (make sure to warn them about the spreading habit!)

Grow in Containers

For very aggressive spreaders like the cultivars ‘Lucifer’ and ‘George Davison’, I recommend growing them in containers. This restricts the stolons and prevents rampant spread.

Plant a few corms in a roomy pot with drainage holes using a quality potting mix. Situate the container in a sunny, well-drained spot. One pot per variety is plenty – crocosmia will quickly fill out its allotted space.

Use Physical Barriers

Installing physical barriers can help impede those questing stolons. Try sinking a vertical root barrier or plastic edging around clumps to contain them. Or plant in a sunken bottomless bucket or pot with just the foliage poking out the top.

For mass plantings, lay thick black plastic under the soil surface to block stolon growth. Just be sure to leave access points to reach in and dig up the clump occasionally.

Choose Less Invasive Varieties

Crocosmia cultivars vary widely in their wandering ways. If you love the look but hate the spread, try these better-behaved options:

• ‘Solfatare’ – sulfur-yellow flowers on short stems
• ‘Severn Sunrise’ – glowing apricot blooms on compact plants
• ‘Star of the East’ – low-growing with orangey-red flowers

The species Crocosmia masoniorum is another non-spreading alternative that opens its orange and yellow blooms sequentially for a longer display.

Be Ruthless!

Finally, don’t be afraid to be brutal if crocosmia invades planted beds or borders. Rip it out, corms and all, if it’s encroaching on areas you want clear. Replant with other perennials that can outcompete it, like daylilies or ornamental grasses.

Keep removing regrowth for a season or two and it will eventually die out. Just stay vigilant to prevent it creeping back from any remaining traces of corms or stolons.

While crocosmias are fabulous plants, their enthusiastic spreading habit can quickly get out of control. With constant monitoring, regular digging and dividing, and implementing barriers, you can keep them contained and enjoy their fiery floral displays without them taking over your garden.

It may seem like an endless battle against the creeping crocosmia, but with persistence and determination, you can gain the upper hand. Just remember to enlist help from family or friends when tackling large infestations – reining in a jungle of unruly crocosmia is definitely a two person job!